Adaptive Friction Compensation for Bi-Directional, Low-Velocity Position Tracking

N.E. Leonard and P.S. Krishnaprasad

In Proceedings of the 31st IEEE Conference on Decision and Control, December, 1992, p. 267-273.


This paper presents a comparative investigation of friction-compensating control strategies designed to improve low-velocity position tracking performance in the presence of velocity reversals for servomechanisms. The methods considered include adaptive control and estimation-based control. Additionally, the various controller designs incorporate different friction models ranging from classical friction and Stribeck friction to the less popular Dahl friction model. This investigation of friction models is motivated by the fact that there is little consensus in the literature on how best to model friction for dynamic friction compensation. The control strategies are compared in an extensive test program involving sinusoidal position trajectory tracking experiments on a direct-drive dc motor. We focus attention on comparative experimental results of friction compensation especially with repeated velocity reversals. The results show that the adaptive and estimation-based controllers outperform more traditional linear controllers. The experiments also yield insight into the appropriateness of the different friction models under the tested operating conditions. {\em In particular, the Dahl model, typically ignored in the literature, proves to be significant for the friction-compensating control problem with repeated zero-velocity crossings. }

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